Dave: Here is some research (other than my own) that substantiates the effectiveness of using curved flight lines along with convergent oblique photos. Please note that the use of curved flight lines is particularly effective for longer, narrower target areas. Just to illustrate the use of curved flight lines for larger areas, I’ve included two illustrations: a) traditional (linear/parallel) flight lines over a glacier and b) curved flight lines over the same glacier.
Minimising systematic error surfaces in digital elevation models using oblique convergent imagery
Jim H. Chandler
First published: 16 March 2011
Results of the simulation process, the laboratory test and the practical test are reported in this paper and demonstrate that an oblique convergent image configuration eradicates the systematic error surfaces which result from inaccurate lens distortion parameters. This approach is significant because by removing the need for an accurate lens model it effectively improves the accuracies of digital surface representations derived using consumer‐grade digital cameras. Carefully selected image configurations could therefore provide new opportunities for improving the quality of photogrammetrically acquired data.
Note: The curved flight lines can be combined (with the eccentricity altered to accommodate the particular aircraft/drone used and/or pilot preference) to create particularly efficient flight paths - with no turnout loops. Refer to the third example/illustration.
This last example is for an open-pit copper mine with an area of about one square mile. It can be flown a) end-to-end by combining opposing convergent flight lines or b) using complete loops - flying complete circuits.